What is an example of a microaggression or covert racism in this chapter?

At a PTA meeting that night, Superintendent Cook makes a speech expressing his sadness with recent unrest at school; he says the security increase is a response to the violence. Shana takes the stage, insisting the guards use intimidation and violence to target minority students. Dr. Cook gives an evasive response. A white woman then makes a speech, saying minority students have gang affiliations and threaten the safety of students like her child. Jay goes up next, recounting Bri's experience with the guards; instead of protecting the children, the guards have threatened them. The guards and the white woman's speech are examples of micro aggression.